I think this is a 4 Turn solution:
T1: G: - : buy Dev
T2: GDev: Dev (G to Kc/Gov) : -
T3: DevKcGov: Kc -> Gov (gain 2G, draw 2G) -> Dev (G -> Kc/Gov): buy Wt
KcGov(top)KcGovDevWtG
T4: KcGov???: Kc -> Gov (gain G, draw to KcGovDevWtGG, gain G) -> Kc -> Dev (G to Kc/Gov, G to Kc/Gov, Gov to Iw/G) -> Wt (draw KcKcGovGovIwG; G in discard) -> Kc -> Kc -> Iw (gain Dev, Brg, Iw) ->
Hand:GovGovG Discard:GDevBrgIw
Gov (gain G, draw to GovGGGDevBrgIw) -> Dev (3G to Kc/Cr, Kc/Mrk, Kc/Fst; stack Kc/Cr/Kc on top) -> Gov (+3 cards)
Hand BrgIwKcKcCr Deck top MrkKcFst
-> Kc -> Kc -> Brg -> Iw (gain Brg, Brg, Kc) -> Cr (draw MrkKcFstBrgBrgKc) -> Kc -> Kc -> Brg -> Brg -> Mrk -> Fst
Total buys: 17; Total cost reduction: 9; Total coin: 14
Total VP bought: 8 Provinces, 5 Fairgrounds, 1 Duchy, 1 Estate = 82 VP
The all colonies version:
Follow as above until:
Hand:GovGovG Discard:GDevBrgIw
Gov (gain G, draw to GovGGGDevBrgIw) -> Dev (3G to Kc/Cr, Kc, Kc/Mrk, Kc/Hwy stack Kc/Cr/Kc on top) -> Gov (+3 cards)
Hand BrgIwKcKcCr Deck top GovKcHwy
-> Kc -> Kc -> Brg -> Iw (gain Brg, gain Brg, gain Kc) -> Cr (draw GovKcHwyBrgBrgKc) -> Kc -> Kc -> Brg -> Brg -> Mrk -> Hwy:
Total buys: 16; Total cost reduction: 10; Total coin: 12
Total VP bought: 8 colonies, 8 provinces = 128 VP